Came across this guy's youtube channel and he seems to know his stuff.  There are other good videos but here's a general one that might be worth watching.

 

 

Excellent video..worth viewing.

 

very informative

This one is pretty good too.  Synchros.

 

 

And this one about GL$/GL5 oils.

 

Excellent videos on the sync rings and the gear oils.  Interesting premise about flow rate in the gear oils.  I think that when I do my 280ZX Turbo transmission, I'll still use GL-5 as the manual recommends.

Actually, Nissan 280ZX turbo transmission fluids have been a point of confusion.  80W-90 or "Dexron", whatever Dexron meant at the time.

Here's 1983.

 Dexron ATF or SAE 80W-90 in a manual gearbox? I hope the explanation can be found in the "for further details, refer to the recommended viscosity chart"

It's been confusing over the whole lifetime of Borg Warner "T5"'s.  Put "atf t5" in the Google box and a ton will come up.  You could read for days and still never be sure.

But the ATF issue still exists.  I bought a 2003 Ford with an M5OD 5 speed in it and Ford recommends Mercon V ATF.  But it got stuck in neutral often (a not uncommon problem with the M5OD.  Too slippery for the synchros?  Don't know), so I used Pennzoil Synchromesh and it fixed all of the problems.  That was 30,000 miles ago and some of the Ford guys say it's going to burn the needle bearings up because it's to thick.  But it's been fine.  

 

17 hours ago, Mark Maras said:

Dexron ATF or SAE 80W-90 in a manual gearbox?

The name DEXRON does not mean it's automaticaly ATF were they talk about i think?  I sure never heard of putting atf in a manual gearbox!

I always use 80w90 oil.

3 hours ago, dutchzcarguy said:

The name DEXRON does not mean it's automaticaly ATF were they talk about i think?  I sure never heard of putting atf in a manual gearbox!

It's right there in the graphic that I pasted from the 1983 FSM.  I doubt that they were recommending gear oil in their automatic transmissions.  

Look at the graphic.  "Type DEXRON" is mentioned twice.

 

 By 83 Dexron was ATF. In the early days of ATs 20w oil (often engine oil) was used and about as thick as automatic trans oil got.